Conditions for growing these favored nuts are one reason their geography is so limited. During their active productive season they need hot hot climates, preferably over 95 - 100 F - but with low humidity for optimal results. They should be planted in Full Sun. They also need a dormancy where temperatures dip below 40 - 45 F for the winter season. Few will survive frigid winters. They are drought tolerant so long as the temperature is in the right vicinity. If you do not live in an arid semi-desert climate region, you can still grow pistachios, just not the common varieties.
There are some varieties that lay claim to being cold hardy. Uzbek pistachio trees, it is claimed, will withstand temperatures down to 10 F degrees below zero as well as hot, dry temperatures and conditions. They are not as productive as those favored by commercial growers but still yield a harvest hefty enough for most home growers.
Uzbek Pistachio, as well as all Pistachios, need at least two trees to set fruit. They are not self pollinating, they must be cross pollinated, both male and female flowers are needed. They are also wind pollinated which means they need to be fairly close, within a few yards of one another to ensure adequate pollination.
Pistachios are little different from other fruit trees so far as pruning is concerned. Proper Pruning enhances the trees overall health and vitality and helps the tree to produce a higher quality pistachio nut.
Young trees should be pruned to no more than 5 primary branches which will serve as the framework or scaffold for all future growth. They provide the structure for the tree. The branches you choose should be equally spaced and be no lower than 2 - 3 feet from the soil surface.
In the early Summer, prune the scaffold branches to a length of 2-3 feet, this will promote side branches. Pistachio trees should have an open center structure as the tree matures and grows taller . Some people like to prune out the upper branches that create a canopy and provide unwanted shade to the tree trunk. This practice is not necessary and has disadvantages. Because of their fruiting and growth habits, pistachio trees will generally naturally open up and allow ample sunlight into the canopy center for fruit-wood production.
When watering, as they are semi-desert plants, you should allow the soil to dry out completely - not slightly moist or a tad wet - but completely dry between watering. Too little water in the case of Pistachios is better than too much. If they are receiving too much moisture the first sign you may notice is a yellowing of the leaves. If they are receiving too little you may notice a slight wilting of the foliage which is easier to correct.
Fertilizer in the trees first season is not necessary. Starting in the second spring a balanced fertilizer such as 10-10-10 is advisable. Avoid high nitrogen fertilizers and by all means fertilize modestly not excessively. No fertilizer is better than too much.
Harvest your nuts in mid to late summer. The hull should be loose and fall from the tree with a shake. A mature pistachio tree can produce upwards of 50 lbs. of nuts in a single season but be advised that Pistachios tend toward biennial bearing, producing a hefty crop one season followed by a scant crop or none at all the next. Nut production is of course also influenced by climatic conditions.